Depends. There are many different kinds. Sometimes it is genetic due to discolored pigment which can probably even be treated with a cosmetic laser procedure. Other times it is due to the shape and depth of your eyes, in this case there isn't much that can be done but you can use a good concealer. Make Up Forever makes an amazing waterproof concealer that does wonders for me, I recommend it. You can buy it at a Sephora store.
Sometimes it is just due to lack of sleep..in that case try to sleep more. Lack of sleep will always aggravate dark circles but some people are more prone to have them than others. I'm fairly prone so when I don't sleep my undereyes look like crap, but other people who aren't prone only have a slight shadow under their eyes from not sleeping.
believe it or not, dark circles under the eyes are most times hereditary and other times not or combined-non-hereditary and hereditary, therefore, there isn't a lot that you can do to treat them as much as you want to. You can use treatments or creams that would "reduce" the look of dark circles but you will never get rid of them. My best bet would just to use concealer. The worse the dark circles, the fuller the concealer coverage should be.
Ok this will not get rid of them but it will make them almost invisible if you do it right :) this will only work if your on the beach or go to tanning salons (please don't) anywhooo you put a SPF of 30 or 15 whatever you go for on your body and face avoiding your dark circles and then on the dark circles you put an SPF 50 :) this worked for me
Cream for dark circles is made especially for protecting and nourishing the vulnerable skin under your eyes. This product is made for correcting and diminishing visible eye aging signs through diminishing the appearance of dark circles. Cream for dark circles is a product that contains special ingredients that can help in lessening the dark circles under eyes through making sure that the skin and the blood vessels underneath are well protected.